Several possible mechanisms by which cells of the distal tubule control net potassium secretion and net potassium reabsorption will be studied in the mammalian kidney. Such renal mechanisms as changes in 1) intracellular potassium concentration, 2) in cell membrane permeability to K, 3) in transepithelial electrical potential, 4) in active reabsorption mechanism and 5) in distal flow rate have been proposed as being capable of modifying K transport. Experiments will be done using micropuncture, microperfusion, tracer flux and electrophysiological techniques to determine which of these mechanisms are actually operative in producing the increased distal K secretion known to follow acute potassium infusions in potassium adapted animals (previously fed a high K or low Na diet) and the decreased distal K secretion known to follow chronic potassium depletion.